(1) Field of the Invention
The invention relates to an enclosure for a semiconductor device, and more particularly, to a combined enclosure and heat sink formed without an adhesive layer.
(2) Description of the Prior Art
Many electronic devices, such as integrated circuits, solid state power amplifiers, and antennas produce substantial amounts of heat when in service. The heat must be re-distributed and, ultimately, conducted away, or the resulting temperature rise may result in the maximum operating temperature limit of the electronic device being exceeded. Therefore, it is often necessary to provide a heat sink structure to conduct away heat from the electronic enclosure used to house the integrated circuit.
Referring now to FIG. 1, an exemplary, prior art semiconductor enclosure 14 with a heat sink 18 attached using an adhesive layer 22 is illustrated. The integrated circuit device 10 is secured to the enclosure 14. The enclosure 14 typically comprises a material with a low coefficient of thermal expansion to match that of the semiconductor material of the integrated circuit 10. In addition, the enclosure must provide protection against moisture and other atmospheric conditions. The enclosure may also need to prevent interference between internal and external signals. By comparison, the heat sink 18 typically comprises a material having a high thermal conductivity and, typically, including heat dissipating fins 24. However, the heat sink 18 and enclosure 14 may have very dissimilar coefficients of thermal expansion. During thermal cycling events, wherein the temperature of the structure rises and falls by a substantial amount, large thermal stresses are created in the adhesive layer 22. Thermal cracking may occur in the adhesive layer 22 due to this thermal cycling.
Referring now to FIG. 2, a cross sectional view of a prior art enclosure 34 with a heat sink 42 attached using an adhesive layer 38 is illustrated. The enclosure is attached to a printed circuit board (PCB) 50. In this example, the integrated circuit chip 30 is sealed with a glass layer 54. Optical fiber 46 is connected to the chip 30 through the enclosure 34. Once again, thermal cycling can cause failure of the adhesive layer 38 to heat sink 42 interface 58.
Several prior art inventions describe packaging enclosures and heat sinks. Japanese Patent 7,321,261A discloses a low-cost tungsten alloy heat sink. The complex shaped, tungsten alloy heat sink demonstrates good heat radiation and thermal conductivity. However, the heat sink must still be bonded to the electronic device to function effectively. U.S. Pat. Nos. 5,878,322 and 5,886,407 disclose heat sinks for microelectronics packages that are formed using powder compacting. However, an adhesive is still needed to bond the heat sink to the enclosure. U.S. Pat. No. 6,075,701 discloses an electronic structure having an embedded pyrolytic graphite heat sink material to enhance the heat dissipating performance. However, the processing parameters limit the range of materials that may be used for the enclosure, or casing. Only low melting point metals, such as aluminum, are compatible with the hot isostatic pressing process. Further, additional heat treatment processing, such as quenching and aging, must be performed to achieve optimum performance.
A principal object of the present invention is to provide an effective and very manufacturable method to form an enclosure for a semiconductor device.
A further object of the present invention is to provide a method for forming an enclosure combined with a heat sink, without a adhesive layer therebetween, to reduce cost and to improve reliability.
A still further object of the present invention is to provide a method to form a combined enclosure and heat sink while maintaining low thermal expansion in the enclosure and high thermal conductivity in the heat sink.
Another further object of the present invention is to provide a method to form a combined enclosure and heat sink where a hollow, cooling channel is formed in the heat sink to further improve the heat sink thermal conductivity.
Another still further object of the present invention is to provide a method to form a combined enclosure and heat sink with a hollow, cooling channel where the cooling channel is formed by the same sintering process used to form the combined structure.
Another object of the present invention is to provide an improved enclosure and heat sink structure.
In accordance with the objects of this invention, a method to form a combined enclosure and heat sink structure for a semiconductor device is achieved. A first feedstock comprising a first mixture of powdered metal materials, lubricants, and binders is prepared. A second feedstock comprising a second mixture of powdered metal materials, lubricants, and binders is prepared such that the difference between the sintering shrinkage of each of the first and second feedstocks is less than 1%. The first and second feedstocks are pressed to form a first green part having an enclosure shape and a second green part having a heat sink shape. The lubricants and the binders from the first and second green parts are removed to form a first powdered skeleton and a second powdered skeleton. The first and second powdered skeletons are sintered to complete the combined enclosure and heat sink structure. The first and second powdered skeletons are in intimate contact during the sintering. Optionally, at least one hollow cooling channel is formed in the combine structure by burning away a fugitive plastic structure during the sintering process.
Also in accordance with the objects of the present invention, a combined enclosure and heat sink structure for a semiconductor device is achieved. The structure comprises an enclosure comprising a first material and a heat sink comprising a second material. The enclosure and the heat sink are coupled together by a sintering process. Optionally, the combined enclosure and heat sink structure contains at least one, hollow, cooling channel.